1. Field of the Invention
The present invention relates to a dental implant. More specifically, this invention relates to an endosteal root-form implant system with hydraulic and mechanical means to mimic the movement and shock-absorbing characteristics of natural teeth.
2. Brief Description of the Prior Art
Since the dawn of civilization, man has been concerned with the partial or total lack of teeth: first for aesthetic, then for practical reasons.
The study of Egyptian mummies from the Middle Kingdom up to the Ptolemys showed unusual processes of dental implantation. Some had substitutions derived from the cadaver,s teeth or sculptured ivory taken from the tusks of different animals. This practice was maintained through medieval times.
A scientific breakthrough in the area of dental implants was achieved by Professor Per-Ingvar Branemark and co-workers. By combining a two-stage surgical technique with the use of titanium fixtures, these scientists achieved predictable results in surgical placement of endosteal-route-form implants. In their continued studies in the early 1960s, these same scientists laid the foundation for modern implantology.
However, because of the lack of periodontal ligaments between the bone and the titanium fixture, such prior art implants do not have the natural motion and shock-absorbing capability of natural teeth.
Screw attachments have been used as shock absorbers but under stress tend to fracture. In a publication entitled "Dental Implant Prosthodontics" (J. B. Lippincott Company 1991 ISBN 0-397-51045-4), one of the authors, Ronald P. Desjardins, observes, "The most common prosthesis problem that the author has thus far noted is the loosening or breakage of the gold locking screw with the resultant loosening of the prosthesis."
In the early 1970s, Dr. Kirsch from Germany designed an implant system called IMZ with a plastic shock-absorber called IME. This device provided elastic properties similar to the periodontal ligament. The IME, an inside and outside threaded intermediary sleeve, is installed inside of the implant by screwing it into the threaded bore of the bone fixture. The sleeve itself has an internal threaded bore, into which a prosthesis is screwed.
However, in the same publication mentioned above, this time Robert J. Chapman observes, "The IME must be replaced every year or two, however, because it is plastic and will deteriorate somewhat with function." That deterioration of the plastic sleeve opens a way for bacteria and changes the mechanical characteristics of this device. U.S. Pat. No. 4,622,010 describes a similar device that avoids the threads on the plastic sleeve.
U.S. Pat. No. 4,993,950 describes a keeper system which uses an 0-ring "to permit universal `rocking` motion of the keeper member relative to the true transmucosal cuff."
U S. Pat. No. 5,006,068 describes a dental implant system with a resilient force-dampening means on the prosthesis itself.
These prior art designs provide only a single means of shock-absorbing capacity. They fail to imitate the longitudinal movement of natural teeth. Prior art implant systems also fail in other respects. Such systems feel unnatural to the person using such prior art dental implant systems when the prosthesis is cemented between a natural tooth abutment and an implant abutment. Furthermore, the cement will be placed under great torquing stress at both ends of the prosthesis. This torquing stress tends to break the cement and cause the failure of the prosthesis.
An important safety feature of the natural tooth has been overlooked by the prior art. If by accident a natural tooth receives a frontal impact which is strong enough to put in jeopardy the integrity of the jaw bone, nature has chosen to loose one or more teeth to preserve the integrity of the jaw bone from major damage.
An object of the present invention is to provide a dental implant system which is able t relieve the prosthesis when impacted by excessive force.
A further object of the present invention is to provide an implant system which mimics the shock-absorbing capabilities of natural teeth, including mimicking the loosening of tooth from the jaw bone.
A further object of the present invention is to provide an implant system which mimics the longitudinal movement of natural teeth.
A still further object of the present invention is to provide a reliable implant system which is safe and relatively inexpensive to manufacture.